Optimization of Spray Parametrs for High Velocity Oxy-Fuel (HVOF) Sprayed Abradable Coating

Abstract

Abradable coating acts as a seal between the blades and casing of aircraft or gas turbine engine. The clearance between the blades and casing should be as small as possible to increase the efficiency of turbine engine. Abradable coatings are engineered to minimize this gap and to enhance the engine performance. During its operation blade tips may rub the stationary casing due to either thermal expansion or misalignment, this will cause wear to blade tip. Abradable coatings act as sacrificial layer between blade and casing and are soft enough to avoid significant wear to blade tips. The coating should not only be soft enough to be scraped easily without damaging the blade tip (good abradability) but also should have high resistance against erosion by the high speed gas flow and solid particles in gas (erosion resistance).Therefore the abradability and the erosion resistance are the most important properties of the abradable coating. But both properties are contradictory and the coating should provide a good balance between the abradability and erosion resistance. The thermal sprayed abradable coatings has been used because of its simple manufacturing process, easy repair of the components, easy adjustment of its properties and good sealing effectiveness. In this work, an attempt has been made to determine the influence of spray parameters like oxygen flow rate, fuel flow rate and spray angle on the erosion resistance and hardness of abradable coating produced by HVOF (High Velocity Oxy-Fuel). Optimum values of these parameters are identified for attaining better erosion resistance and low hardness of coating by the application of Taguchi method.

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